1.Examine the heater for leaks. Water may not be visible because it evaporates as it escapes, so check for signs of cracking around the check valve itself. Oxygen in the system often causes squeaking, squealing and other noises that indicate a problem.

2.Verify the area around the check valve is properly secured. Longer pipes vibrate if not bracketed, and so squeaking often results. Use a stud finder to locate a solid part of the wall closest to the check valve, and then drill a bracket into the stud with screws to prevent that section of the system from vibrating.